The present invention relates generally to an automated surface inspection system and, more particularly, a system and method for detecting defects on a painted surface of a workpiece.
Demand for higher quality has pressed manufacturers of mass produced articles, such as automotive vehicles, to employ automated manufacturing techniques that were unheard of when assembly line manufacturing was first conceived. Today, robotic equipment is used to assemble, weld, finish, gauge and test manufactured articles with a much higher degree of quality and precision than has been heretofore possible. Computer-aided manufacturing techniques allow designers to graphically conceptualize and design a new product on a computer workstation and the automated manufacturing process ensures that the design is faithfully carried out precisely according to specification.
Quality control is also an important component of the automated manufacturing process. For instance, rather than employing human inspectors, automated surface inspection systems are used to perform repetitive visual inspection of a workpiece in order to detect flaws in the surface of a workpiece.
An imaging device is typically used in an automated surface inspection system to capture frames of image data representative of a portion of the surface of the workpiece. To determine what constitutes a surface defect, the surface inspection system compares the location of a potential surface defect from frame to frame. In the conventional case, the surface inspection system assumes that the inspection surface is substantially planar, and thus the potential surface defect is moving at the same or proportional rate (in relation to the imaging device) at which the workpiece is being translated by the movable member. However, for contoured inspection surfaces, the potential surface defect does not travel at the same rate in relation to the imaging device as the velocity of the movable member. As a result, conventional surface inspection systems are unable to accurately compare the location of a potential defect between frames, and thus may be unable to identify surface defects in contoured inspection surfaces.
Therefore, it is desirable to provide an automated system and method for detecting defects in a contoured surface of a workpiece. To the extent that the inspection surface is painted, it is also desirable that the surface inspection system distinguish surface flaws caused by dirt, pinholes or scratches from the surface roughness of the paint (i.e., "orange peel") on the workpiece. It would further be advantageous if such a system were able to characterize the defects by size so that only those body parts having defects larger than a certain threshold size would need to be rejected by the inspection process.